Such a defibrillator is disclosed in U.S. Pat. No. 6,397,104 B1, for example. The defibrillator makes provision for an electrocardiograph. The electrocardiograph allows the cardiac electric activity of a patient to be recorded. On the basis of the cardiac electric activity, it is possible to detect a cardiac arrest, ventricular fibrillation, irregular heart rhythms or myocardial infarctions. The known defibrillator has a disadvantage in that myocardial infarctions, in particular imminent or silent myocardial infarctions, cannot be dependably and reliably detected.